Expansion system for asphalt plant oil heater

ABSTRACT

An oil expansion system for an asphalt plant closed loop oil heater wherein a body of inert gas is maintained in contact with the surface of the oil in the oil heater to inhibit the oxidation of the oil. The inert gas in the oil heater tank communicates through a conduit with the upper portion of a lower expansion chamber partially filled with liquid, and the liquid in the lower expansion chamber communicates through a second conduit with an upper expansion chamber at a higher level, so that the rising and receding level of oil in the heater tank due to thermal expansion and contraction displaces the inert gas to the lower expansion chamber, and the inert gas, in turn, displaces the liquid from the lower portion of the lower tank to the upper tank, causing the inert gas to be trapped between the two bodies of liquid.

[451 July 31, 1973 1 EXPANSION SYSTEM FOR ASPHALT PLANT OIL HEATER [75] Inventor: James Donald Brock, Chattanooga,

Tenn.

[73] Assignee: CMI Corporation, Oklahoma City,

Okla.

22 Filed: Feb. 24, 1972 21 Appl. No.: 228,861

[56] References Cited UNITED STATES PATENTS 2,636,490 4/1953 Miller 126/3435 A 2,112,733 3/1938 Bumham 165/106 X 1,833,719 11/1931 Moody 165/106 X 3,111,935 11/1963 Loebel 126/3435 A X 3,457,523 7/1969 Wesselink 165/108 X Primary ExaminerWilliam F. O'Dea Assistant Examiner-Peter D. Ferguson Att0rneyDunlap, Laney, Hessin & Dougherty [57] ABSTRACT An oil expansion system for an asphalt plant closed loop oil heater wherein a body of inert gas is maintained in contact with the surface of the oil in the oil heater to inhibit the oxidation of the oil. The inert gas in the oil heater tank communicates through a conduit with the upper portion of a lower expansion chamber partially filled with liquid, and the liquid in the lower expansion chamber communicates through a second conduit with an upper expansion chamber at a higher level, so that the rising and receding level of oil in the heater tank due to thermal expansion and contraction displaces the inert gas to the lower expansion chamber, and the inert gas, in turn, displaces the liquid from the lower portion of the lower tank to the upper tank, caus ing the inert gas to be trapped between the two bodies of liquid.

3 Claims, 1 Drawing Figure PAIENIEB JUL 3 I ma 5n mm mm J 1 j NN QN/ O- m mm nw 5 ml 3 PN mm .Erm ..N \\\\\\N\ EXPANSION SYSTEM FOR ASPHALT PLANT OIlL HEATER BACKGROUND OF THE INVENTION In an asphalt mix preparation plant where hot bituminous liquid is mixed with an aggregate filler to form hot asphalt mix, it is necessary to keep the bituminous liquid hot prior to mixing with the filler, and to keep the asphalt mix hot until it is dispensed to a transport vehicle for transporting to the construction site. While various methods have been used to keep the bituminous liquid and asphalt mix at the proper temperature, the most commonly used method is to heat oil or a similar liquid and pass the hot oil in a closed loop system in the walls of the bituminous liquid containers, asphalt mix storage silos, mix conveyors, and various other elements of the asphalt plant where the mix or the bituminous liquid is likely to become cold. While the oil heating systems used for this purpose are closed loop sys tems with a substantially constant weight of oil maintained in the system at all times, the oil of the system as well as the tanks, conduits, pumps and other elements used in the system expand and contract so that the space required to contain the oil varies. For instance, when the closed loop oil heating system is not in operation and the oil is cold, the oil contracts and occupies a smaller space in the system. When the oil heating system is activated and the oil is heated from atmospheric temperature to operation temperature at about 300 F the oil expands and a larger space in the closed loop system is required to contain the oil.

In the past, various expansion systems have been utilized to compensate for the thermal expansion and contraction of the oil of an oil heating system. These systems typically comprise an expansion tank positioned above the heat exchanger and in communication with the upper portion of the heat exchanger. The expansion tanks were arranged to receive the overflow oil from the heat exchanger or oil heating tank when the system was hot and the oil had expanded, and subsequently to direct the oil back to the heating tank when the oil in the heating system had cooled and contracted. The overflow expansion tank systems of this type allow the oil discharged thereto to become cold, and when the oil is subsequently passed back to the hot heating tank, the oil is again heated. In addition, the overflow expansion systems allow the oil to be contacted by air from the atmosphere. The continual heating and cooling of the overflow oil and the continuous contact of the overflow oil with oxygen in the air causes the oil to oxidize and otherwise deteriorate, and a sludge or layer of congealed oil forms in the overflow expansion tank. The sludge is sometimes carried back into the heating tank from the overflow expansion tank and passes with the hot oil in the oil heating system through the closed loop conduits of the heating system. The sludge frequently constricts and blocks the flow channels of the closed loop system.

SUMMARY OF THE INVENTION Briefly described, the present invention comprises an expansion system for an asphalt plant closed loop oil heater which prevents the oil in the system from oxidizing or becoming otherwise contaminated. A body of inert gas is maintained in contact with the oil in the heating tank of the closed loop system, and when the oil in the system becomes hot, expands and displaces a portion of the inert gas, the inert gas passes to the upper portion of an expansion chamber. The gas in the expansion chamber displaces a liquid from the lower portion of the expansion chamber to a higher level. When the oil in the closed loop system cools and contracts, the liquid in the upper expansion tank flows back under the influence of gravity to the lower portion of the expansion tank and displaces the inert gas back from the upper portion of the lower expansion tank to the oil heating tank. The inert gas is thus maintained in continuous positive pressure contact with a surface of oil in the closed loop oil heating system, and the oil from the closed loop system never leaves the closed loop system to become cold.

Thus, it is an object of the present invention to provide an expansion system for an asphalt plant. closed loop oil heating system wherein the oil does not tend to become contaminated;

Another object of the present invention is to provide an inexpensive expansion system for a closed loop liquid heating system wherein the expansion and contraction of the liquid in the heating system is compensated for substantially without contamination of the liquid.

Another object of the present invention is to provide a method and apparatus for heating bituminous liquid and asphalt mix in an asphalt mix preparation plant.

Other objects, features and advantages of the present invention will become apparent upon reading the following specification, when taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the drawing comprises a schematic illustration of an oil heating system for an asphalt preparation plant, with only the oil heater and expansion tank arrangement being illustrated.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now in more detail to the drawing, an oil heating system 10 for an asphalt preparation plant (not shown) comprises oil heating tank 11 and expansion tank 12. Oil heating tank 11 includes an oil inlet 14 and an oil outlet 15, and pump 16 is connected to oil outlet 15. The outlet of pump 16 communicates with the closed loop conduit system of the asphalt preparation plant and urges the hot oil from oil heating tank 11 to the bituminous storage tank, asphalt mix storage hopper, and the various other elements of the asphalt preparation plant (not shown) which must be maintained at a high temperature. The oil from the closed loop system is routed back through the oil inlet 14 to the oil heating tank 11.

Burner 18 communicates with burner tubes 19 inside oil heating tank 11. Burner 18 receives air from conduit 20 and natural gas, fuel oil or other combustible fluid from conduit 21 and ignites the combustible mixture. The mixture is directed through the burner tubes 19 in a multiple pass arrangement inside oil heating tank 1 l, and the gases from the burner tubes 19 are exhausted through an upwardly extending stack 22. The burner tubes function so that the oil circulating through the closed loop oil heating system is maintained at the desired temperature. For instance, the oil circulating from the oil heating tank 11 through the closed loop system will leave the oil heating tank at approximately 350 F.

Expansion tank 12 comprises a horizontal internal partition 24 which divides the expansion tank into lower chamber 25 and upper chamber 26. First conduit means 27 extends from the upper portion of oil heating tank ll through the lower wall 28 of expansion tank 12 up into the upper portion of lower chamber 25. Second conduit means 29 extends from the lower portion of upper chamber 26 through partition 24 in a downward direction to the lower portion of lower chamber 25. Vent tube 30 opens through the upper wall 31 of expansion tank 12 and communicates the upper portion of upper chamber 26 with the atmosphere.

A body 32 of inert gas, such as Nitrogen, is located inside oil heating tank 11 and is normally disposed above the level of the oil in the tank. The gas is able to pass through the first conduit means 27 back and forth between the upper portion of lower chamber 25 of expansion tank 12 and the upper portion of oil heating tank 11. A body of liquid 33 is maintained in the lower portion of lower chamber 25 of expansion tank 12 and is able to pass back and forth through second conduit means 29 between the lower portion of lower chamber 25 and the lower portion of upper chamber 26. The liquid 33 can comprise various different liquids, but in the present embodiment of the invention the liquid 33 is identical to the oil in the closed loop oil heating system. Thus, if the liquid 33 should inadvertently become mixed with the oil circulated through the closed loop oil heating system, there will be no contamination of the oil in the closed loop system.

When the closed loop oil heating system is placed in operation, burner 18 is activated to heat the burner tubes 19, so that the burner and its burner tubes function as heating means to heat the body of oil 35 in the oil heating tank 11. Pump 16 is activated and functions as circulation means to circulate the oil from the oil heating tank through the closed loop system. As the oil circulates through the system, the hot oil passing from the oil heating tank 11 through pump 16 is replaced by cooler oil received from oil inlet 14 from the closed loop system. As the temperature of the oil increases, the oil in the closed loop system expands, and the surface 36 of the body of oil in the oil heating tank rises. For instance, the surface 36 may be at level A when the oil heating system is cold, and may rise to level B when the system is in operation and the oil is hot. The inert gas 32 in the upper portion of oil heating tank 1 l is displaced from the upper portion of the heating tank as the surface of the oil rises, and the gas passes in an upward direction through first conduit means 27 to the upper portion of lower chamber 25. The surface 36 of the body of liquid 33 in the lower chamber 25 of expansion tank 12 will be at level A when the oil in the closed loop system is cold. As the oil in the closed loop system is heated and expands, the inert gas passing from oil heating tank 11 through first conduit means 27 into the upper portion of lower chamber 25 displaces the body of liquid 33 in the lower chamber 25 so that the level 37 moves in a downward direction from level A toward level B. The liquid 33 which is displaced from lower chamber 25 moves in an upward direction through second conduit means 29 to upper chamber 26 which is at a higher level than lower chamber 25. The surface 38 of the liquid in upper chamber 26 will be at level A when the oil in the closed loop oil heating system is cold, and when the oil in the closed loop heating system expands to displace the gas from the heating tank to the expansion tank, the level 38 will rise from level A to level B. The air above the liquid in the upper chamber 26 is vented to the atmosphere through vent tube 30.

When the oil heating system is shut down by extinguishing burner 18 and allowed to cool, the oil in the closed loop system will contract and the surface of the oil in oil heating tank 11 will tend to recede from level B to level A. As the space available for the inert gas in oil heating tank 11 increases, the liquid in upper chamber 26 of expansion tank 12 flows under the influence of gravity from the higher level of the upper chamber 26 in a downward direction through second conduit means 29 into the lower portion of lower chamber 25. The inert gas in the upper portion of lower chamber 25 is thus displaced from the upper portion of lower chamber 25 in a downward direction through first conduit means 27 back into the upper portion of oil heating tank 11.

If the closed loop oil heating system should be overfilled with oil so that upon heating of the oil all of the gas from the upper portion of the heating tank is displaced from the heating tank and a portion of the oil from the closed loop system is also displaced through first conduit means 27 to the expansion tank 12, the inert gas will be trapped in the upper portion of lower chamber 25 while the excess oil will fall to the lower portion of the lower chamber 25 and become mixed with the body of liquid 33 in the expansion tank. When the closed loop oil heating system is subsequently shut down and the oil of the system is allowed to cool, the additional space in the upper portion of the oil heating tank which is created by the contraction of the oil will become occupied by the inert gas in the manner previously described. Thus, throughout the nonnal operation of the closed loop oil heating system a continuous supply of inert gas will be maintained in contact with the surface of the oil in the oil heating tank, and no cold oil will be introduced to the oil heating tank.

While this invention has been described in detail with particular reference to a preferred embodiment thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinbefore and as defined in the appended claims.

I claim:

1. In a closed loop liquid heating system for an asphalt preparation plant or the like comprising tank means through which the liquid circulates, heating means for heating the liquid in said tank means, and circulation means for passing the liquid from said tank means through a closed loop heat exchange system and back to said tank means, the improvement therein comprising expansion means including a lower chamber normally partially filled with liquid and partially filled with gas and an upper chamber positioned above said lower chamber, first conduit means connecting the upper portion of said tank means with the upper portion of said lower chamber, and second conduit means connecting the lower portion of said lower chamber with the lower portion of said upper chamber, whereby upon an increase in the level of the liquid in said tank means the gas above the liquid in said tank means is displaced from the upper portion of said tank means through said first conduit means to the upper portion of said lower chamber and the liqud in the lower portion of the lower chamber is displaced by the gas from the lower portion of the lower chamber through said second conduit means to the lower portion of said upper chamber, and upon a decrease in the level of the liquid in said tank means the liquid from the lower portion of said upper chamber flows through said second conduit means to the lower portion of said lower chamber and displaces the gas in the upper portion of said lower chamber through said first conduit means to the upper portion of said tank member.

2. A closed loop liquid heating system comprising tank means normally partially filled with liquid and through which the liquid is circulated, fire tubes extending through said tank means for heating the liquid in said tank means, a lower chamber partially filled with liquid, an upper chamber positioned above said lower chamber, first conduit means communicating with the upper portion of said tank means above the level of the liquid in said tank means and with the upper portion of said lower chamber above the level of the liquid in said lower chamber, and second conduit means communicating with the lower portion of said lower chamber below the level of the liquid in said lower chamber and with the lower portion of said upper chamber.

3. A method of maintaining a body of inert gas in closed communication with the surface of a body of hot oil in a heating tank partially tilled with oil of an oil heating system comprising passing the gas displaced from the upper portion of the heating tank upon an increase in oil level in the heating tank to the upper portion of a chamber partially filled with liquid, and pass ing the liquid displaced from the chamber from the lower portion of the chamber to a higher level; and upon a decrease in oil level in the heating tank, passing liquid from the higher level to the lower portion of the chamber and passing the gas from the upper portion of the chamber to the upper portion of the heating tank. 

1. In a closed loop liquid heating system for an asphalt preparation plant or the like comprising tank means through which the liquid circulates, heating means for heating the liquid in said tank means, and circulation means for passing the liquid from said tank means through a closed loop heat exchange system and back to said tank means, the improvement therein comprising expansion means including a lower chamber normally partially filled with liquid and partially filled with gas and an upper chamber positioned above said lower chamber, first conduit means connecting the upper portion of said tank means with the upper portion of said lower chamber, and second conduit means connecting the lower portion of said lower chamber with the lower portion of said upper chamber, whereby upon an increase in the level of the liquid in said tank means the gas above the liquid in said tank means is displaced from the upper portion of said tank means through said first conduit means to the upper portion of said lower chamber and the liqud in the lower portion of the lower chamber is displaced by the gas from the lower portion of the lower chamber through said second conduit means to the lower portion of said upper chamber, and upon a decrease in the level of the liquid in said tank means the liquid from the lower portion of said upper chamber flows through said second conduit means to the lower portion of said lower chamber and displaces the gas in the upper portion of said lower chamber through said first conduit means to the upper portion of said tank member.
 2. A closed loop liquid heating system comprising tank means normally partially filled with liquid and through which the liquid is circulated, fire tubes extending through said tank means for heating the liquid in said tank means, a lower chamber partially filled with liquid, an upper chamber positioned above said lower chamber, first conduit means communicating with the upper portion of said tank means above thE level of the liquid in said tank means and with the upper portion of said lower chamber above the level of the liquid in said lower chamber, and second conduit means communicating with the lower portion of said lower chamber below the level of the liquid in said lower chamber and with the lower portion of said upper chamber.
 3. A method of maintaining a body of inert gas in closed communication with the surface of a body of hot oil in a heating tank partially filled with oil of an oil heating system comprising passing the gas displaced from the upper portion of the heating tank upon an increase in oil level in the heating tank to the upper portion of a chamber partially filled with liquid, and passing the liquid displaced from the chamber from the lower portion of the chamber to a higher level; and upon a decrease in oil level in the heating tank, passing liquid from the higher level to the lower portion of the chamber and passing the gas from the upper portion of the chamber to the upper portion of the heating tank. 